Thermal dye sublimation printers or photo printers for example have a resolution of 300 dpi and for example 255 different color intensities per pixel. Thereby very good image qualities can be generated, whereby absolutely no screening can be seen. This results from the fact that in thermal sublimation printing a dye of a waxy consistency is used. By high temperatures of ca. 300° C. or more the wax is transformed into a gaseous phase in which it can be vapor deposited. To do so in practice individual partial areas of a print head are heated in order to partially evaporate dyes from a carrier foil, which then are transferred onto the paper. On the basis of temperature the quantity of the dye to be transferred can be specified, and in this way the brightness or color intensity of the pixel concerned can be varied. As this is theoretically infinitely variable possible, a great color depth and color saturation can be generated; in practice in most cases discrete heating values are specified, for example 255 different heating values. Also individual pixels are not distinguishable. On the other hand however there are high investment and/or operating costs.
Compared with this are current ink printers or inkjet printers, for example with piezo print heads, indeed cheaper. Here the printing process is controlled either by individual electrostatic charging of a continuous inkjet, which then, depending on its electrostatic charge, can be deflected in a field (continuous inkjet method, CIJ), or by dispensing individual drops as required (drop-on-demand method, DOD). Such printers however master only 2 or 3 color intensities per each printing color. While this becomes hardly noticeable especially when printing out text or other black and white documents with a strong contrast between bright and dark, inkjet printers are less suitable for printout of color photographs. In order to be able to use them as photo printers anyway, it was already tried to improve the intrinsically unsatisfactory color rendering of inkjet printers by partitioning each individual pixel into a small screen of, for example, 4 times 4 smaller dots then followed by printing 0, 1, 2 . . . 15, 16 of those small screen dots, so one can then already—at a rather macroscopic inspection—distinguish 16 different color intensities. The problem however is that these smaller brightness screen dots of a pixel are indeed still perceived by the eye as dots or anyway as a visual disturbance. Even worse, in case of pixels of exactly the same color a then always repeating screen dot arrangement would lead to a so-called moiré effect, i.e., the microscopic structures are regularly repeating and thereby generating a clearly perceptible or even unmissable macroscopic pattern.
A method conforming to its genre for example is revealed in document EP 0 899 937 A2. There inks of the gray shades 0, 80, 130, and 255 are used whereat in a color intensity interval between 0 and 80 only inks with the gray values 0 and 80 are used proportionately, in a color intensity interval between 81 and 130 inks with the gray values 80 and 130 are used, and so forth. However it is relatively complicated here to arrive at the proportionate shares of two inks of different brightness values or respectively intensities starting from a color value of an image; that requires among other things matrix calculations, in particular computations by means of a so-called dithering matrix. For example when an ink of a color intensity of 130 is more intensive by the factor 1.625 against an ink having a color intensity of 80 so that the allocation of appropriate quantities in a drop turns out to be complex.
From these disadvantages of the described state of technology resulting is the problem initiating the invention to advance an ink or inkjet printer to such an extent, or to develop a printing method suitable for ink or inkjet printers so that thereby also such printers can be utilized as photo printers with an optimum of color depth.